It is not self-evident. Islam could become the dominant Religion and not really change much at all or it could be very Fundamentalist. Hell, it could become the dominant Religion and still be a Minority of the population.
Islam by nature is domineering, and it encroaches upon several important aspects of human existence so I can't imagine things not changing much at all compared to the status quo..
If you look at the history of Islam pertaining to conquering and settling non Muslim lands, one repeating pattern asserts itself. Muslims are agreeable and pliant when greatly outnumbered, but as their numbers continues to grow, they become far more aggressive and demanding, to the point of complete and utter intolerance once they have enough strength to gain control..
